This invention relates to ultrasonic equipment for measuring the propagation velocity of an ultrasonic pulse wave propagating within a blood vessel so as to make continuous measurement of absolute blood pressure.
There is known a technique for measuring the propagation velocity of the pulse, wave (called pulse wave speed) on the basis of the deformation of blood wall or of the time lag between blood flow Doppler signal waveforms at two far-separated points. For example, an ultrasonic pulse wave speed estimator is described in JP-A-62-26050. According to this speed estimator, information related to changes of reflected ultrasonic waves with respect to time is obtained at two points on the blood wall along the pipe, a time difference between the changes at the two points is measured from this information and the pulse wave speed is calculated on the basis of the time difference and the distance between the two points.
Also, a B-mode interlocking-type ultrasonic small displacement measuring instrument is described in Inst. Elec. Inf. Com. Eng. Tec. Rep., MBE 84-17, pp. 9-16 (1984). According to this document, the phase of echo signal is followed by use of a zero-crossing point tracking function and a very small displacement of tissue is measured to thereby obtain physical information such as hardness as well as morphologic information. As is described in the above document, this instrument is also used to make non-invasive measurement for local blood vessel elasticity, or blood vessel elasticity distribution using the pulse.
In addition, measurement of mean pulse wave speed in artery throughout body by use of ultrasonic Doppler blood flow wave is described in Proc. of Jpn. Soc. Ultrason. Med. 51-PB-31, pp. 231-232 (Nov. Showa 62 (1987)). According to this document, the pulse waves in carotid artery and femoral artery are simultaneously recorded, the mean pulse wave speed calculated by use of the time difference therebetween is compared with that of blood flow wave recorded at the same position.